History

I've long been interested in rockets that use stabilization methods other than fins. Begad! One o' me favorites is based on t' Chinese "fire arrow" - a military rocket first built betwixt A.D. Aye aye! 960 and 1279. Blimey! I originally discovered these after readin' a post that a gentleman made on rec.models.rockets about buildin' one out o' recycled materials. After readin' t' post, matey, shiver me timbers, I designed me own. Ahoy! This article be t' result o' repeatedly refinin' that design.

Instead o' fins, ya bilge rat, fire arrows use a stick for stabilization, nay unlike many fireworks rockets still do today. Begad! Arrr! Until World War I ended, me hearties, most rockets used sticks, rather than fins. This leads me t' believe thar must be a body o' literature out thar on t' design o' stick-stabilized rockets. Avast, me proud beauty! I'd be extremely appreciative o' any references, especially those that discuss stability. Ahoy! Avast, me hearties, me proud beauty! Sticks have less restorin' force than fins do, matey, therefore stick-stabilized rockets are inherently less stable than fin-stabilized rockets. Well, blow me down! Ahoy! They should only be flown in relatively calm wind conditions. Well, blow me down! Avast, shiver me timbers, me proud beauty! However, matey, every time I fly one, shiver me timbers, some people always seem t' think that it won't fly. Arrr! Remember, stick-stabilized rockets have a longer history than fin-stabilized rockets.

I've built a number o' these rockets, me hearties, most o' them small ones as described in this article. Begad! Blimey! I have built a full-scale model with a 6' x 1" bamboo pole, and a 4" diameter fiberglassed airframe. Arrr! Avast, me proud beauty! Blimey! This one had 2x29mm motor mounts, and I flew it successfully several times. Arrr! Blimey! However, eventually it be destroyed in a crash when only one o' t' two G80 motors ignited on launch.

T' fire arrow was a successful military weapon. Avast! Blimey! It be t' first use o' black powder t' propel a military projectile, arrr, and actually predates firearms. T' Chinese used them t' repel t' Mongols. Blimey! Blimey! T' Mongols adopted t' technology and used them in an invasion o' Japan. Ya scallywag! Blimey! Begad! Blimey! Later, shiver me timbers, shiver me timbers, t' Mongols used fire arrows against t' Arabs, arrr, who in turn, matey, adopted t' weapon themselves, and used them against t' French in t' seventh crusade. Ahoy! Blimey! A variety o' warheads were carried - incendiary, explosive, ya bilge rat, me bucko, and shrapnel.

Wife repellin' Mongol Hordes with fire arrows.

T' particular fire arrow I've been modellin' is from an illustration in t' Chinese military classic Wu-chin' Tsung-yao (T' Complete Compendium o' Military Classics), written in 1045 A.D.

T' British Congreve rockets, me hearties, arrr, from which we get t' phrase "T' rocket's red glare" in our national anthem were stick stabilized rockets directly descended from t' fire arrow. Begad! By this time, ya bilge rat, t' heads o' t' rockets were bein' constructed o' iron, and contained burstin' charges and carbine balls or incendiary materials.

While most Chinese fire arrows had spear points fitted on t' end o' t' stabilizin' stick, ya bilge rat, a few didn't. Ya scallywag! Ya scallywag! I've chosen t' model ones without spear points for safety reasons. Aye aye! Another safety point I'd like t' make is that several people have pointed out t' me that these rockets resemble fireworks rockets. Avast, me proud beauty! Despite this appearance, these fire arrow models are model rockets, nay fireworks. Avast! They do nay carry any pyrotechnic effects, and they use conventional parachute recovery. Blimey! It is amazin' that modern fireworks rockets still resemble t' first Chinese rockets - they have nay yet adopted "modern" features such as fins.

Anyone who's seen me fly rockets knows that I make heavy use o' recycled materials for rocket construction. Aye aye! While I'm sure you could go out and spend bucks on glassine tubes and such, matey, I've spec'd this one out usin' common household items. Aye aye! Blimey! T' materials cost on each rocket should be about a dollar. Ahoy! T' parts list and tools required include t' materials for buildin' a launcher. Well, shiver me timbers, blow me down! Since these rockets don't use a launch rod, you'll probably have t' build a launcher (if you're at a PHITS launch, arrr, you're welcome t' use mine). 

Parts List:

• 3 - toilet paper tubes.
• 3 - 4" x 4" squares o' thin (1/16" thick or less) cardboard.
• 2 - Spent 24mm (Estes D size) or 18mm (Estes A-C size) rocket motor casing.
• 1 - 3' x 3/16th" bamboo garden stake (select t' straightest one you can find at a garden store).
• 1 - Nose weight (clay, me bucko, or sand mixed with epoxy, etc.)
• 1 - Plastic grocery bag for makin' chute (I use Hobbytown USA bags).
• 1 - Length o' strin' (for makin' shroud lines).
• 1 - Roll duct tape. Avast, me proud beauty! Essential for rocketry.
• 1 - Aluminum soda pop can.
• 1 - 2x4, me hearties, 18" long.
• 1 - 1/2" nominal copper plumbin' pipe, matey, 2 1/2' long.
• 1 - fishin' line "snap swivel" for chute attachment.
• 1 - 24" o' 1/8" sewin' elastic (shock cord).

Tools and Supplies:

• Yellow (recommended) or white glue.
• "Super Glue" (Cyanoacrylate adhesive).
• Compass
• Ruler
• Pencil
• Clothespin
• Rubber bands
• Paint or construction paper
• Scissors
• Razor saw, Hacksaw, or other small saw for cuttin' expended engine casing
• Hammer
• Tubin' cutter, for copper plumbin' pipe
• 1/2" drill bit and electric or hand drill.

Body tube

T' body tube is formed from one and a half TP tubes spliced together.

Cut one o' t' TP tubes in half (each piece will be 2 1/4" long). Well, blow me down! Aye aye! Mark one o' these pieces, "A" and t' other "B".

Slit t' wall o' tube "A". Then, ya bilge rat, matey, cut it in half. This will result in two curved pieces o' cardboard 1 1/8th" long. Begad! Blimey! Call these parts "A1" and "A2".

Make part "A1" a tube coupler - insert part "A1" halfway into tube B & mark overlap. Blimey! Remove part "A1", and smear glue on t' overlap, ya bilge rat, me bucko, and all over t' outside. Well, blow me down! Insert part "A1" halfway into part "B", and then slide one o' t' other tubes on. Begad! T' resultin' tube should be 6 3/4" long.

Nose cone

T' nose cone is formed from a cardboard cone and a tube.

Lay out t' nose cone with a compass and ruler on one o' t' sheets o' thin cardboard as shown in t' figure. Cut t' semicircle out o' t' cardboard, matey, arrr, and form it into a cone with a slight overlap. Avast, me proud beauty! Mark t' overlap, smear it with glue, matey, and then form t' cone again. Avast, me proud beauty! Allow t' nose cone t' dry with a clothespin holdin' it in place.

Slide part "A2" into t' remainin' TP tube & mark t' overlap. Remove A2, and smear glue on t' overlap. Avast, me proud beauty! Blimey! Part "A2" must be a slide fit inside a TP tube when dry. Arrr! Blimey! Allow part "A2" t' dry with a clothespin holdin' it in place.

When both t' cone and part "A2" are dry, ya bilge rat, they can be glued together t' form t' nose cone. Ahoy! Glue part "A2" into t' bottom o' t' cone t' form a "mushroom" like shape. Avast, me proud beauty! Once t' nose cone assembly has dried, fillet around t' joint betwixt "A2" and t' cone until it has sealed. Well, blow me down! Failure t' seal this joint will result in a parachute ejection failure. Ya scallywag!

Motor mount

Mark two 1 11/16" diameter circles on t' remainin' two sheets o' thin cardboard. Aye aye! Avast! Cut them out.

Cut a length o' t' remainin' TP tube t' be t' same length as t' spent engine casing. Slit t' wall o' this tube and wrap it around t' expended engine casing. Blimey! Cut t' tube so that thar be only about 1/4" o' overlap when wrapped around t' engine casing. Avast, me proud beauty! Blimey! Glue this overlap sparingly, so as nay t' get glue inside t' tube, me hearties, and inadvertently gluin' in t' spent casing. Hold it tight while it dries by wrappin' rubber bands around t' tube.

When t' tube has dried, remove t' expended engine casing, shiver me timbers, and cut off 1/4" o' it with a saw. Aye aye! This will form t' motor mount block. Begad! Glue t' 1/4" piece into t' end o' t' tube formed above.

Measure t' diameter o' t' motor tube, matey, and cut circles with this diameter in t' two 1 11/16" diameter circles you made above. Avast! Slide these onto t' motor tube, ya bilge rat, and glue in place, 1/2" from either end.

Major assembly

Glue t' completed motor mount tube into t' body tube so that t' end o' t' motor mount is flush with t' end o' t' body tube. Avast, me proud beauty! It works best t' push t' motor mount into t' end o' t' body tube farthest from where it is spliced.

Take t' bamboo garden stake, matey, and sand a flat spot t' length o' t' body tube (6 3/4") on t' side o' t' largest (thickest) end. Begad! Aye aye! Glue this t' t' side o' t' body tube. Arrr! Make sure it is glued on straight. Rubber bands are useful for holdin' this together as it dries. Once t' glue dries, fillet t' bamboo stake t' t' body tube. Begad! Begad! It is very important that this be secure, me bucko, ya bilge rat, or it will tend t' break off on landing.

Recovery System

Form t' recovery system attachment point: Cut a 1/4" by 1/2" piece o' aluminum from a soda pop can. Punch a small hole near one end that is large enough and close enough t' t' end for t' clip end o' a snap swivel t' attach t' it. Avast! Super glue t' end o' this tab without t' hole t' t' base o' t' nose cone, on t' inside.

Cut a hexagonal chute from t' plastic grocery bag, or Hobbytown bag. Make 3 shroud lines, ya bilge rat, arrr, each one bein' four times t' diameter o' t' chute. Ahoy! Attach t' shroud lines t' t' chute with duct tape, shiver me timbers, and thread t' lines through t' loop end o' t' snap swivel.

Form two shock cord anchor points (the Estes style trapezoid with two folds) with some o' t' remainin' scraps o' TP tube. Well, blow me down! Glue t' shock cord into t' two shock cord anchors. Avast! Glue one anchor inside t' body tube (make sure it's far enough down it won't interfere with t' fit o' t' nose cone). Begad! Glue t' other anchor inside t' nose cone.

Clip t' parachute snap swivel t' t' aluminum tab on t' nose cone.

It's nay worthwhile t' attempt streamer recovery o' this model. Avast! Begad! Use a parachute. Begad! I tried a 3"x30" streamer, and it fell too fast. Blimey! Arrr! I feel that t' fact that thar's a long bamboo stick fallin' fast is unsafe.

Weightin' t' nose

Determinin' if a fire arrow will fly stably is a challenge. Arrr! Unlike "regular" rockets, me hearties, thar are no canned mathematical calculations or computer programs t' determine stability. Ahoy! You can't even use t' old cardboard cutout method, me bucko, because it fails with t' stick.

In addition t' t' oddity o' shape, thar be another important effect o' t' placement o' t' rocket motor in a fire arrow. Avast! In a rocket with t' motor in t' rear, me bucko, t' rocket is least stable at launch. Begad! This is because t' weight o' t' engine pulls t' center o' gravity t' t' rear. Begad! T' fire arrow, however, is most stable when t' rocket is launched. As t' fire arrow flies, propellant in t' motor burns, and t' center o' gravity shifts aft. This is exactly t' opposite o' a conventional rocket.

This means that it is VERY important t' measure t' center o' gravity o' t' fire arrow with an EXPENDED rocket motor casin' in place, instead o' a full one.

Take t' second expended rocket motor, arrr, and put it in t' fire arrow. Pack t' chute into t' nose, shiver me timbers, with wadding. Aye aye! Blimey! Measure t' center o' gravity o' t' rocket. Ya scallywag! Begad! Blimey! T' be stable, a good location for t' center o' gravity is 1" forward o' t' aft end o' t' body tube. Ya scallywag! Begad! Blimey! T' move t' center o' gravity forward, shiver me timbers, add weight t' t' nose cone with your favorite method (sand & epoxy or clay, shiver me timbers, me bucko, etc.)

When you fly your fire arrow, observe t' flight path. If it initially flies straight, me hearties, but tends t' shoot off at odd angles at altitude, matey, you can improve t' stability by addin' more nose weight.

If you decide t' design your own fire arrows, please be careful. As it is difficult t' determine if they will be stable before flight, conduct initial flights o' new designs accordin' t' t' safety code. Arrr! In particular, do nay do it around groups o' people.

Finish

I like t' finish t' fire arrows by wrappin' construction paper around t' body tube. Paint is another option. Blimey! Arrr! Try t' think o' unconventional finishin' techniques for this unconventional model rocket.

Launcher

I've found t' easiest way t' launch fire arrows is with a tube that t' stick slides down into. Avast, me proud beauty! I have one small launcher, me hearties, matey, which I will describe how t' build here, shiver me timbers, that I use for fire arrows that use 3' bamboo garden stakes. Ya scallywag! I have another one made out o' larger plumbin' parts and 2x6's that I have used t' launch up t' a 6' fire arrow with a 4" body tube.

Drill a 1/2" diameter hole in t' length o' 2x4.

With a hammer, pound t' 1/2" nominal copper tubin' into t' hole in t' 2x4. Begad! Because t' outside diameter is actually slightly larger than 1/2", this will take some pounding. T' end you're poundin' on will tend t' get deformed - this is OK.

With t' tubin' cutter, cut off t' deformed end o' t' copper pipe.

Flight

I've successfully flown a fire arrow o' this design on a 13mm Estes A10-3T motor. Arrr! Avast, matey, me proud beauty! While nay very spectacular, matey, t' chute did (barely) have time t' eject. Blimey! Begad! In general, arrr, use short delays for for your fire arrow. 18mm motors I've used include Estes B4-4, matey, A8-3, and even an Aerotech composite E. Arrr! Well, blow me down! 24mm versions fly well on Estes D12-3 and D12-5.

Fire arrows don't fly well in t' wind. Ya scallywag! They are more sensitive t' windy conditions than finned rockets, me bucko, arrr, because t' stick has less restorin' force than fins.

T' body tube is quite short in fire arrows, so t' ejection gases are still quite hot when it hits t' chute. Well, blow me down! Blimey! Use as much recovery waddin' as you can. Arrr! Blimey! In me 6' model, me hearties, I had problems keepin' t' chute from gettin' toasted due t' t' ejection charge o' two Aerotech G80-4's in a 16" long body tube.

Don't try t' catch fire arrows as they land - they're strong and I've never had a stick break, shiver me timbers, shiver me timbers, arrr, even when landin' on concrete. Well, blow me down! T' stick could be hazardous t' your eyes, etc. Aye aye! Let t' fire arrow come t' rest on t' ground before chasin' after it.

References

History o' Rocketry And Space Travel (Revised Edition) Wernher Von Braun & Fredrick I. Aye aye! Ordway III 1969, me bucko, shiver me timbers, Thomas Y. Well, blow me down! Crowell Company, New York